C.M. Fang

Electronic structure of the misfit layer compound (SnS)1:20TiS2: band structure calculations and photoelectron spectra

In order to understand the electronic structure of the incommensurate misfit layer compound (SnS)1:20TiS2 we carried out an ab initio band structure calculation in the supercell approximation. The band structure is compared with that of the components 1T-TiS2 and hypothetical SnS with a similar structure as in (SnS)1:20TiS2. The calculations show that the electronic structure is approximately a superposition of the electronic structures of the two components TiS2 and SnS, with a small charge transfer from the SnS layer to the TiS2 layer. The interlayer bonding between SnS and TiS2 is dominated by covalent interactions. X-ray and ultraviolet photoelectron spectra of the valence bands are in good agreement with the band structure calculation.

Electronic structure and magnetic properties of KCrSe2

characterized by x-ray powder diffraction is a layered compound isostructural with : a = 3.80 A; c = 22.19 A; space group . The magnetic properties are similar to those of but with an even more pronounced difference between the intralayer and interlayer exchange interactions of localized moments. The magnetic susceptibility above 100 K is of a Curie - Weiss nature; the Curie temperature is +250 K. An antiferromagnetic transition with K occurs; in the ordered state, ferromagnetic layers are coupled antiferromagnetically. The analysis showed the intralayer exchange interaction and interlayer exchange interaction to be 16.7 K and -0.06 K, respectively. A band-structure calculation using the LSW method was performed for in the ferromagnetic state (neglecting the interlayer antiferromagnetic ordering). The calculations show that is a semiconductor with a band gap of 0.7 eV. The potassium atoms are nearly ionized. The Cr states are completely spin polarized. The electronic configuration of Cr is , with a local magnetic moment of per Cr atom.

Crystal structure and band structure calculations of Pb1/3TaS2 and Sn1/3NbS2

Abstract The crystal structures of Pb 1 3 TaS 2 and Sn 1 3 NbS 2 were determined using single-crystal X-ray diffraction. The space group is P6322 and the unit cell dimensions are: a = 5.759(1), c = 14.813(1) A and a = 5.778(1), c = 14.394(1) A , for the Pb and Sn compounds, respectively. The post-transition metal atoms occupy one-third of the trigonal-antiprismatic holes between sandwiches NbS2 and TaS2. The Nb and Ta atoms are in trigonal-prismatic coordination by sulfur atoms. The stacking of sandwiches is the same as in 2H disulfides. The arrangement of the post-transition metal atoms is different for the two compounds. A bond valence calculation showed Sn and Pb to be divalent. Ab initio band structure calculations were performed for Sn 1 3 NbS 2 using the localized spherical wave method, and for Pb 1 3 TaS 2 with the augmented spherical wave method with spin-orbital interactions included. The calculations show that the rigid band model is approximately valid for the electronic structures; the main difference with those of 2HNbS2 and 2HTaS2 being the presence of Sn 5s and 5p (Pb 6s and 6p) bands and a larger S 3p/Nb(Ta) 4d (5d) gap in the intercalates (1.0 eV for Sn 1 3 NbS 2 , 1.3 eV for Pb 1 3 TaS 2 . The Sn 5s (Pb 6s) bands are at the bottom (bonding) and top (antibonding) of the valence bands which range from about −7 to about 0 eV. The conduction bands are composed of Nb 4dz2 or Ta 5dz2 orbitals hybridized with S 3p. These bands are filled to about 0.3 holes per Nb (Ta), corresponding to a donation of two electrons per Sn (Pb).

Influence of a spin-polarized tip on the Fe(001) surface

A detailed study of ab initio calculations for an iron parallel electrode and a tip–surface system, using the localized spherical wave method and the supercell-slab approach is presented. The calculations show that within the medium inter-electrode distance range (about 2.9 to 5.7 A) the interaction between two parallel electrodes has a strong influence on the local surface electronic structure, while the magnetic moment is almost constant. A tip induces changes of the specific surface states near the Fermi level. However, the spin-polarization of the tip shows no significant influence on the surface states.